1. Field of the Invention
This invention relates to the electrochemical removal of a surface layer from an article, and more particularly but not exclusively to the removal of a defective coating from data storage disc to facilitate recoating.
2. Background Art
A known data disc comprising as substrate a disc of aluminium is approximately 130 mm diameter by 1.9 mm thick when coated. A central aperture of 40 mm diameter penetrates the disc. These data discs are coated overall by a sequence of sputter coating, electroless coating or other plating treatments to create a finished disc having a substrate core disc of aluminium having a zincate treatment on both sides clad by a layer of nickel; a layer of cobalt covering the nickel; a thin (flash) layer of chromium on the cobalt; and outer layer of carbon covering the flash layer of chromium. During manufacture of these discs defects may arise in any of the deposited layers. Current practice is to examine the finished discs and discard any that fail to meet the test criteria.